'\" et
.TH REALPATH "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
realpath
\(em resolve a pathname
.SH SYNOPSIS
.LP
.nf
#include <stdlib.h>
.P
char *realpath(const char *restrict \fIfile_name\fP,
    char *restrict \fIresolved_name\fP);
.fi
.SH DESCRIPTION
The
\fIrealpath\fR()
function shall derive, from the pathname pointed to by
.IR file_name ,
an absolute pathname that resolves to the same directory entry, whose
resolution does not involve
.BR '.' ,
.BR '..' ,
or symbolic links. If
.IR resolved_name
is a null pointer, the generated pathname shall be stored as a
null-terminated string in a buffer allocated as if by a call to
\fImalloc\fR().
Otherwise, if
{PATH_MAX}
is defined as a constant in the
.IR <limits.h> 
header, then the generated pathname shall be stored as a null-terminated
string, up to a maximum of
{PATH_MAX}
bytes, in the buffer pointed to by
.IR resolved_name .
.P
If
.IR resolved_name
is not a null pointer and
{PATH_MAX}
is not defined as a constant in the
.IR <limits.h> 
header, the behavior is undefined.
.SH "RETURN VALUE"
Upon successful completion,
\fIrealpath\fR()
shall return a pointer to the buffer containing the resolved name.
Otherwise,
\fIrealpath\fR()
shall return a null pointer and set
.IR errno
to indicate the error.
.P
If the
.IR resolved_name
argument is a null pointer, the pointer returned by
\fIrealpath\fR()
can be passed to
\fIfree\fR().
.P
If the
.IR resolved_name
argument is not a null pointer and the
\fIrealpath\fR()
function fails, the contents of the buffer pointed to by
.IR resolved_name
are undefined.
.SH ERRORS
The
\fIrealpath\fR()
function shall fail if:
.TP
.BR EACCES
Search permission was denied for a component of the path prefix of
.IR file_name .
.TP
.BR EINVAL
The
.IR file_name
argument is a null pointer.
.TP
.BR EIO
An error occurred while reading from the file system.
.TP
.BR ELOOP
A loop exists in symbolic links encountered during resolution of the
.IR file_name
argument.
.TP
.BR ENAMETOOLONG
.br
The length of a component of a pathname is longer than
{NAME_MAX}.
.TP
.BR ENOENT
A component of
.IR file_name
does not name an existing file or
.IR file_name
points to an empty string.
.TP
.BR ENOTDIR
A component of the path prefix names an existing file that is neither
a directory nor a symbolic link to a directory, or the
.IR file_name
argument contains at least one non-\c
<slash>
character and ends with one or more trailing
<slash>
characters and the last pathname component names an existing file that
is neither a directory nor a symbolic link to a directory.
.br
.P
The
\fIrealpath\fR()
function may fail if:
.TP
.BR EACCES
The
.IR file_name
argument does not begin with a
<slash>
and none of the symbolic links (if any) processed during pathname
resolution of
.IR file_name
had contents that began with a
<slash>,
and either search permission was denied for the current directory or
read or search permission was denied for a directory above the current
directory in the file hierarchy.
.TP
.BR ELOOP
More than
{SYMLOOP_MAX}
symbolic links were encountered during resolution of the
.IR file_name
argument.
.TP
.BR ENAMETOOLONG
.br
The length of a pathname exceeds
{PATH_MAX},
or pathname resolution of a symbolic link produced an intermediate
result with a length that exceeds
{PATH_MAX}.
.TP
.BR ENOMEM
Insufficient storage space is available.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Generating an Absolute Pathname"
.P
The following example generates an absolute pathname for the file
identified by the
.IR symlinkpath
argument. The generated pathname is stored in the buffer pointed to by
.IR actualpath .
.sp
.RS 4
.nf

#include <stdlib.h>
\&...
char *symlinkpath = "/tmp/symlink/file";
char *actualpath;
.P
actualpath = realpath(symlinkpath, NULL);
if (actualpath != NULL)
{
    ... use actualpath ...
.P
    free(actualpath);
}
else
{
    ... handle error ...
}
.fi
.P
.RE
.SH "APPLICATION USAGE"
For functions that allocate memory as if by
\fImalloc\fR(),
the application should release such memory when it is no longer
required by a call to
\fIfree\fR().
For
\fIrealpath\fR(),
this is the return value.
.SH RATIONALE
Since
\fIrealpath\fR()
has no
.IR length
argument, if
{PATH_MAX}
is not defined as a constant in
.IR <limits.h> ,
applications have no way of determining how large a buffer they need
to allocate for it to be safe to pass to
\fIrealpath\fR().
A
{PATH_MAX}
value obtained from a prior
\fIpathconf\fR()
call is out-of-date by the time
\fIrealpath\fR()
is called. Hence the only reliable way to use
\fIrealpath\fR()
when
{PATH_MAX}
is not defined in
.IR <limits.h> 
is to pass a null pointer for
.IR resolved_name
so that
\fIrealpath\fR()
will allocate a buffer of the necessary size.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIfpathconf\fR\^(\|)",
.IR "\fIfree\fR\^(\|)",
.IR "\fIgetcwd\fR\^(\|)",
.IR "\fIsysconf\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<limits.h>\fP",
.IR "\fB<stdlib.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
